Malaria parasites are unable to synthesize purines de novo and rely on the host red blood cell and blood plasma as sources of these materials for their growth and reproduction. The proposed program of study is designed to describe for the human malaria Plasmodium falciparum growing in vitro: 1. The mechanisms of purine transport by the erythrocytic stages, 2. The metabolic conversions of purines, nucleosides, and nucleotides that take place within the red blood cell as the parasite grows and reproduces itself, 3. The purine salvage pathway enzymes of P. falciparum and distinguish these from those of the host cell, 4. The in vitro effects of antimalarials and purine analogs on the growth of the parasite and their effectiveness in blocking purine utilization, and 5. The role exogenous purines may play in improving in vitro growth of P. falciparum.